Remove CONF values from volume clients

To move volume clients to tempest-lib, this patch moves
CONF values from volume clients to the client setting.

Change-Id: Iddd8306723c1ff33105f513c1993a0497a949c29
Depends-on: Ic86739dde83dcac8f68e53599967de53694f692f
diff --git a/tempest/services/volume/json/backups_client.py b/tempest/services/volume/json/backups_client.py
index 102e823..dad5aff 100644
--- a/tempest/services/volume/json/backups_client.py
+++ b/tempest/services/volume/json/backups_client.py
@@ -18,10 +18,9 @@
 
 from tempest.common import service_client
 from tempest import exceptions
-from tempest.services.volume.json import base
 
 
-class BaseBackupsClientJSON(base.VolumeClient):
+class BaseBackupsClientJSON(service_client.ServiceClient):
     """
     Client class to send CRUD Volume backup API requests to a Cinder endpoint
     """